Patent GB-191027696-A (GB)
Title: Improvements in Electric Conversion.
Inventor: CABOT SEWALL
IPC: H02M3/34
Filed: 1910-11-28
Granted: 1911-09-28
Abstract: 27,696. Cabot, S. Dec. 4, 1909, [Convention date]. Commutator switching-arrangements.-A system for the conversion of low-potential electric currents, direct or alternating in character, into high-potential direct currents upon a constantcurrent or constant-potential basis, and capable of inverse operation, comprises an oscillating circuit by means of which a vibratory current in one circuit is transmitted to another from which a continuous current is taken. When the current source is direct in character, an oscillating circuit such as c<1>, l<1> is intermittently disconnected therefrom, and during a definite portion of the cycle of oscillation resulting, this circuit is connected to form another containing additional capacity C' and inductance I<1>, the period of which is considerably higher than that of the circuit c<1>, l<1>. A continuous discharge through a transmission line X is obtained from the condenser C', the voltage of this discharge being of high potential. When the source of current is alternating in character, it is continuously connected to the first-mentioned oscillating circuit. Similar means are used at the other end of the transmission line to reduce the potential to a working value. As shown in Fig. 1, a number of oscillating circuits c<1>, l<1> ... c<10>, l<10> are each connected to earth e and to a lead connected to two brushes b<1>, b<1>1 ... b<10>, b<1>10 respectively. The brushes b<1> ... b<10> are arranged to rub upon a rotating ring R, to which energy is supplied from the direct-current source E by brushes B<1>, B<2>. A gap G of insulating-material is arranged in the ring R, and is so dimensioned as to leave each circuit c<1>, l<1>, &c. unconnected with the source E for half the period of oscillation of these circuits. During this half-period, the energy in such circuit c<1>, l<1> changes from kinetic to static form and back again. At about the end of a quarter-period, when almost all the energy is of static form and consists of a charge in the condenser c<1>, connexion is made between the brush b<1>1 and a projection P<1> on a ring R<1>, to which an inductance L and an earthed capacity G<1> are connected by a brush B<3> which is in continuous contact with the ring. Thus an oscillating circuit c c<1> L<1> C<1> e is formed, and during the time in which the projection P<1> is operative the charge of the condenser c<1> is transferred to the capacity C<1> by the oscillation produced in this circuit. This cycle is repeated as each circuit c<1> l<1> ... c<10> l<10> comes into operation and the condenser C', the capacity of which is large compared to that of the condenser c<1> &c., becomes charged to a high potential by the rapid accessions of charges from the condensers c<1> &c. The speed of the ring is given in one instance as 1800 revolutions per minute when the diameter of the ring R<1> is four feet. The amount of power transmitted by the system will depend partly upon this speed, the number of circuits c<1>, l<1>, &c., and the voltage of the source E. The inductances L<2> are employed, if desired, to assist in maintaining the potential of the line X constant. They have a large inductance compared to that of the coils L<1> should the conditions of the transmission line tend to modify the natural period of the circuit c c' L' C<1> c. The system thus described operates upon a constantpotential basis. The Specification gives the necessary constants for a particular case. To effect conversion on a constant-current basis, the time during which the brush b<1> &c. is out of contact with the ring R is doubled by increasing the gap G. The condenser C<1> may be of the aluminium-film type. In order to prevent sparking at the gap G, a commutator is used having four rings and employing only one condenser such as c<1> &c., preferably with a dielectric of compressed air, with the inductances such as l<1> ; the segments of this commutator are arranged to provide a number of gaps in series, and a high peripheral speed is avoided. Fig. 5 shows the system arranged with a low-potential alternating-current source supplying a synchronous motor A, the secondary circuit of a transformer also supplied thereby including an oscillating circuit C L corresponding to the circuit cl l<1> &c. of Fig. 1. Connexion with the inductance L<1> and condenser C' is made by means of a synchronouslydriven switch comprising a cylinder 2 having two series of segments a, b arranged to bridge the gaps between brushes c, d arranged in two rows on insulating-rods carried by rocker arms 8, 9; the rocker arms 8, 9 are adjusted to make this connexion when the potential of the condenser C almost reaches the maximum in each cycle, the length of the segments being such as to prolong this connexion for a half-period of the circuit C L<1> C<1>. The natural period of the circuit C L is made equal to that of the alternating-current source. A transformer having appreciable magnetic leakage may be employed with this arrangement, and the inductance L omitted.